Expansion tank with a piston

ABSTRACT

The herein described apparatus is a novel expansion tank and method for use with a water system. The housing of the expansion tank contains a spring biased piston. When the water pressure of the system is sufficient to overcome the spring&#39;s resistance, the piston will be compressed against the spring allowing water to flow into the expansion chamber. As the water pressure of the system decreases, the spring will bias the piston towards its rest position and force water from the expansion tank. By using a piston in place of the prior art rubber diaphragm a more robust mechanism to contain water resulting from thermal expansion is provided.

TECHNICAL FIELD

This invention relates generally to water systems and more particularly to a water system expansion tank and method for use with a hot water heater.

BACKGROUND

Modern indoor plumping generally has a backflow preventer installed at or near the water meter to prevent water from a structure's water system from flowing out. The presence of a backflow preventer creates a closed system within the structure where the water system exists. Most interior water systems rely on a hot water heater to provide hot water to the structure. As the water continues to be warmed its density decreases and its volume increases, thereby generating pressure within the hot water heater's tank. To alleviate some of this pressure an expansion tank is made apart of the system thus providing more volume to contain the heated water. Without the expansion tank, pressure within the hot water heater can increases until the structural integrity of the heater is compromised. If the hot water heater becomes structurally compromised then severe water leakage can occur. Thus, the need for an expansion tank on closed water systems is known in the prior art.

An expansion tank is typically linked by a pipe to the hot water heater. The expansion tank is designed to contain excess water which is the result of thermal expansion. Thermal expansion occurs as a result of water being heated in the tank of the hot water heater. A prior art expansion tank typically uses a rubber diaphragm to divide the tank. One side of the tank is designed to receive expanding water from the water system to which it is attached. The other side of the diaphragm contains air under pressure. Water is not compressible, while air is. When heated water enters the expansion tank due to the resulting increase of water pressure it causes the diaphragm to flex against and compress the air cushion thereby allowing water to enter the tank. When the water system is opened through the use of a faucet or similar device, or the water cools, water leaves the tank and returns to the water system at large. This cycle occurs at a minimum, as frequently as the burner of the hot water heater is activated. As the rubber diaphragm flexes repeatedly under routine use it eventually tears or is otherwise compromised. Once the diaphragm wears out or ruptures the system fails resulting in pressurized water being expelled from the system into the surrounding area. The water leak could result in expensive water damage being caused to both the dwelling and other property contained therein. The cost of repair for such damage can range from $5,000-$70,000, or even more, with the average claim for water damage being $15,000 according to State Farm Insurance. As such the need for an expansion tank with a more robust means of receiving and releasing pressurized water exist.

An object of the present invention is to provide an expansion tank which overcomes the deficiencies found in the prior-art rubber diaphragm with a more robust spring-operated piston mechanism to regulate the flow of water into and out of the expansion tank.

SUMMARY

The preferred embodiment of the present invention consists of a cylindrical housing which has an extension at one end that is configured to be connected to a water system. The interior of the cylindrical housing contains an aluminum piston which is in contact with the interior walls of the housing, effectively dividing the housing into two separate areas. The piston has two o-rings that occupy parallel planes about its periphery. The o-rings serve the purpose of preventing water from seeping around the face of the piston and collecting behind it, within the spring compartment. The walls of the housing are lubricated with an insoluble lubricant. The piston is acted on by a spring thereby pressing the piston towards the extension located at the bottom of the housing. The area between the back of the piston and the interior of the cylindrical housing contains the spring and is vacuum sealed. This area is generally referred to as the spring compartment. The piston face has a quasi-crescent shape which creates an air gap between itself and the water system. As expanding water enters through the provided opening into the interior of the cylindrical housing, the piston and spring are compressed thereby allowing the water to occupy the interior volume of the provided tank. When the system is opened, or the water cools, pressure within the system is thereby reduced. Water is expelled from the expansion tank once the force of the spring on the piston exceeds the force exerted by the water on the piston. Through the use of a spring powered aluminum piston the inherent weakness of a flexible rubber diaphragm are over come.

The foregoing it a broad outline of the significant features of the present invention, more pertinent and specific details of these features are discussed in the detailed description of the invention that follows. It should be understood by those skilled in the art that the disclosed preferred embodiment may be modified or used as a basis for designing other methods of constructing a similar device which is capable of fulfilling the same purpose. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of preferred and alternative embodiments is better understood when read in conjunction with the appended drawings. For the purposes of illustration, there is shown in the drawings exemplary embodiments; however, the subject matter is not limited to the specific elements and instrumentalities disclosed. In describing the preferred and selected alternate embodiments of the present invention, as illustrated in the Figures, specific terminology is employed for the sake of clarity. The invention, however, is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish similar functions.

FIG. 1 shows a side view of the expansion tank;

FIG. 2 shows a cutaway view of the expansion tank shown in FIG. 1;

FIG. 3 shows the cutaway view of FIG. 2 with the piston compressing the spring;

FIG. 4 shows a side view of the expansion tank installed on a hot water heater; and

FIG. 5 shows an alternative embodiment of the expansion tank.

FIG. 6 shows an additional alternate embodiment of the expansion tank.

It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended to define the limits of the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

Turning now to the figures in which like reference characters indicate corresponding elements throughout the several views, there is shown an expansion tank, generally designated by reference numeral 10, which consists of a cylindrically shaped housing, generally designated by reference numeral 20, that contains a piston 30 which is biased into position by a spring 50. The expansion tank is configured to be connected to a water system 60 through a threaded extension 28. As used herein, the word “bottom” corresponds to the portion of the housing 20 where the threaded extension 28 is located as shown in FIG. 1; “top” corresponds to the portion of the housing 20 which is opposite the threaded extension 28, also shown in FIG. 1.

Shown in FIG. 1 is an illustration of the expansion tank 10 wherein an embodiment of the cylindrical housing's 20 exterior is shown. The side of housing 20 which is not shown in the drawing is substantially identical to the view therein illustrated. In general the housing is constructed from a stainless steel alloy, but other material compositions which are suitable for containing pressurized water that are currently in use or may come into use would make acceptable substitutes. At the bottom of the housing is a threaded extension 28 which in the preferred embodiment has ¾ inch threads configured to interface with a pipe fitting and thereby connect the housing 20 to a water system 60. The threaded extension 28 can easily be configured with an array of thread pitches which are suitable for use in securing an expansion tank 10 to a water system 60.

FIGS. 2 and 3 show cutaway view of the expansion tank 10 illustrated in FIG. 1. The housing 20 consists of a top tank portion 44 and a bottom tank portion 46. The interior of the housing 20 is divided into two general sections by the piston 30. The piston 30 is constructed from aluminum and has a face 32 which has a quasi-crescent shape. The backside 40 of the piston 30 is smooth in the preferred embodiment. It should be known that any metallic compound or synthetic material which is suitable for use as a piston in an aqueous environment would be an acceptable substitute from which to manufacture the piston 30. Located about the periphery of the piston 30 are two grooves 36 each of which houses an o-ring 38. The area between the backside 40 of the piston 30 and the top of the housing 20 is the spring compartment, while the area between the face 32 of the piston 30 and the bottom of the housing 20 is referred to as the water pocket 24. A spring 50 is in operational contact with the backside 40 of the piston 30 and is wholly contained within the spring compartment 22 of the housing 20. The spring 50 places 80 lbs of force against the backside of the piston 30. Further, the spring compartment 22 is isolated from the water pocket 24 through the use of o-rings 28 present about the exterior of the piston 30 and as a result of the close fit between the piston's 30 exterior and the interior of the housing 20. Present, but not illustrated, is an insoluble lubricant which is used on the interior walls of the housing 20 to aid the piston 30 during its movement cycles. Located near the top of the housing 20 is a port 42 which is used during assembly to vacuum seal the spring compartment 22.

The spring 50 used with the preferred embodiment expansion tank 10 has a max load of 80 lbs and is manufacture from a stainless steel. It should be understood that any material suitable for use as a spring may be substituted. Further, the load weight of the spring may be selected based on the pressure generated by the water system 60 to which the expansion tank 10 is being incorporated.

FIG. 2 shows the piston 30 being biased into position against the bottom of the housing's 20 interior, as is the case when no water is present within the interior of the expansion tank 10. FIG. 3 shows the piston 20 compressed towards the top interior portion of the housing 20, as is the case when sufficient pressure is generated by the water system 60 to force water into the expansion tank 10.

FIG. 4 shows a side perspective view of the expansion tank 10 installed on a water system 60. The housing's 20 interior is placed into communication with the water system 60 through the threaded extension 28 located on the bottom of the housing 20. The threaded extension 28 consists of a cylindrical tube which is hollow that has at least a portion of its exterior threaded. The water system 60 generally consists of a hot water heater, pipes, water which originates from a well or municipal water system and a series of faucets or other pressure release mechanisms.

The expansion tank 10 is assembled as follows. The bottom tank portion 46 and the top tank portion 44 are lubricated with an insoluble lubricant. An o-ring 38 of appropriate size is selected and placed into the o-ring grooves 36 present about the exterior side wall of the piston 30. Next, the piston 30 is placed into the interior of the bottom tank portion 46 and oriented such that its face 32 is oriented towards the bottom. The area between the face 32 of the piston 30 and the threaded extension 28 of the bottom tank portion 44 is generally referred to as the water pocket 24. A spring 50 is placed on top of the piston 30 and then covered by the top tank portion 44. Where the top tank portion 44 and the bottom tank portion 46 meet a seam is formed. At the seam the two tanks portions 44, 46 are welded together to form the housing 20 of the expansion tank 10. The area between the backside 40 of the piston 30 and the interior of the housing 20 is generally referred to as the spring compartment 22. Through the use of the port 42 located on the top tank portion 44 of the housing 20 the spring compartment 22 is vacuum sealed. It is to be understood that the spring compartment 22 does not have to be vacuumed sealed during assembly. Other ways of vacating air from the spring compartment 22 which are within the scope of the present invention are described in, but not limited to, those methods outlined in the alternate embodiments below.

In operation the housing 20 is threadedly secured to the water system 60 by the threaded extension 28, but other method routinely used to secure pipes together offer acceptable alternatives. After initial installation, water faucets may be opened to allow for air trapped in the water pocket 24 of the housing's 20 interior to be released from the water system 60 as a whole. The hot water heater has a thermostat which automatically activates a burner or series of burners to heat water contained within a tank. As the water heats it gradually expands through a phenomenon known as thermal expansion. This expansion of the water increases the internal pressure of the water system 60 as a whole and results in water being forced through the opening of the threaded extension 28 and into the interior of the housing 20. Initially the piston 30 is biased into its first position by the spring 50, shown in FIG. 2. As water enters the water pocket 24 of the housing 20 sufficient pressure is being generated in the water system 60 to slowly move the piston 30 and thereby compress the spring 50 towards the top of the housing 20, shown in FIG. 3. When the burner of the hot water heater shuts off, a faucet is opened, or another exit is provided the water from the water system 60, pressure within the water system 60 will decrease resulting in water flowing out of the expansion tank 10. Water is able to exit the expansion tank 10 when the force applied by the spring 50 to the backside 40 of the piston 30 is greater than the pressure of the water against the piston face 32.

FIG. 5 shows an alternate embodiment of the expansion tank 100. This embodiment is constructed substantially similar to the preferred embodiment expansion tank 10 except for the presence of an air release valve 110. The air release valve 110 is located on the housing 112 and provides an exit for air trapped within the spring compartment 22. Air is vented from the spring compartment 22 through the release valve 110 as the piston 30 is compressed as a result of water entering the expansion tank 110. This removes the need to vacuum seal the spring compartment during manufacturing.

FIG. 6 shows an additional alternate embodiment of the expansion tank 200 would have a check valve 210 which has been incorporated on the face 222 of a piston 220 which has been appropriately modified. The check valve 210 is oriented such that the valve flap opens towards the water pocket 24. As the expansion tank 200 receives water from the water system 60 the air pressure within the spring compartment 232 increases. This increase in air pressure is the result of the piston 220 and the spring 50 being compressed. Once sufficient pressure has been generated within the spring compartment 232 air is released into the water pocket 24 as a result of the cracking pressure of the check valve 210 being overcome.

The foregoing description and drawings comprise illustrative preferred and alternate embodiments of the present invention. Having thus described exemplary embodiments of the present invention, it should be noted by those skilled in the art that the within disclosures are exemplary only, and that various other alternatives, adaption's, and modifications may be made within the scope of the present invention. Merely listing the steps of the method in a certain order does not necessarily constitute any limitation on the order of the steps of the method. Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing description and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of I imitation. Accordingly, the present invention is not limited to the specific embodiments illustrated herein, but is limited only by the following claims. 

1: An expansion tank for use with a fluid system having variable pressures and a predetermined safe upper-limit pressure, said expansion tank comprising: a housing defining a port, an internal side wall, an external wall, an upper internal space, and a lower internal space, wherein said port is in fluid communication with the fluid system and said lower internal space; a piston slidably carried within said housing having a top surface, a bottom surface and an annular side wall; means for urging said piston toward said lower internal space; wherein when the predetermined safe upper-limit pressure is reached or exceeded within the fluid system, fluid flows through said port into said lower internal space thus urging against said piston and causing said piston to be displaced thereby reducing the pressure within the fluid system. 2: The expansion tank of claim 1, wherein said piston defines said upper internal space and said lower internal space, and wherein said upper internal space is fluidly sealed from said lower internal space; 3: The expansion tank of claim 2, further comprising at least one o-ring positioned on said annular side wall of said piston. 4: The expansion tank of claim 1, wherein said piston has a quasi-crescent shaped bottom surface. 5: The expansion tank of claim 1, wherein said means for urging said piston is a spring. 6: The expansion tank of claim 5, wherein said spring is positioned on said top surface of said piston within said upper internal space. 7: The expansion tank of claim 1, further comprising means for testing the pressure within said expansion tank. 8: An expansion tank for use with a water heater (tank type) having variable pressures and a predetermined safe upper-limit pressure, said expansion tank comprising: a housing defining a port, an internal side wall, an external wall, an upper internal space, and a lower internal space, wherein said port is in fluid communication with the water heater tank and said lower internal space; a piston slidably carried within said housing having a top surface, a bottom surface and an annular side wall; a spring carried on said top surface of said piston within said upper internal space for urging said piston toward said lower internal space; wherein when the predetermined safe upper-limit pressure is reached or exceeded within the water heater, fluid flows through said port into said lower internal space thus urging against said piston and causing said piston to be displaced thereby reducing the pressure within the water heater. 9: The expansion tank of claim 8, wherein said piston face has a concave depression 10: The expansion tank of claim 8, further comprising at least one o-ring positioned on said annular side wall of said piston wherein said upper internal space is sealed from said lower internal space. 11: The expansion tank of claim 8, further comprising means for testing the pressure within said expansion tank. 12: A method of reducing the pressure within a fluid system, comprising the steps of: a) obtaining an expansion tank comprising: a housing defining a port, an internal side wall, an external wall, an upper internal space, and a lower internal space, wherein said port is in fluid communication with the fluid system and said lower internal space; a piston slidably carried within said housing having a top surface, a bottom surface and an annular side wall; means for urging said piston toward said lower internal space; wherein when the predetermined safe upper-limit pressure is reached or exceeded within the fluid system, fluid flows through said port into said lower internal space thus urging against said piston and causing said piston to be displaced thereby reducing the pressure within the fluid system; and b) attaching said expansion tank to be in fluid communication with said fluid system via said port. 13: The method of claim 12 further comprising the step of coating at least a portion of the interior walls of said housing that may come into operational contact with said piston with an insoluble lubricant. 14: The method of claim 12 further comprising the step of vacuum sealing at least a portion of said housing. 